Ferulic acid is a very abundant compound in nature as it is a component of the cell wall of many plant species such as rice, maize and sugar beet, among others. However it is not found in the free form, but forms glucoside links to the carbohydrate chains of the cell wall as a result of which both enzyme and alkaline hydrolytic methods are used to release it. For example, an enzyme method for obtaining free ferulic acid is described in patent document U.S. Pat. No. 6,143,543.
Patent application WO2004/110975 describes a process for the recovery of ferulic acid in free form from the water used to cook maize known as nejayote resulting from the nixtamalization industry. This process comprises acidifying the nejayote (>pH 4) with a dilute solution (20 to 35%) of sulfuric acid, hydrochloric acid or phosphoric acid to encourage the adsorption of ferulic acid. The ferulic acid is adsorbed with activated carbon, although synthetic resins such as amberlite, polypyrrolidone and divinylbenzene styrene may also be used; this stage can be carried out in a tank with stirring or semi-continuously in packed columns.
When carried out in a stirred tank, stirring takes place at between 100 and 150 rpm for 1 to 8 hours or until ferulic acid adsorption is more than 95%, depending upon the particle size and density of the adsorbent material, at an operating temperature of 20 to 50° C. The adsorbent material is recovered by filtering, settling or centrifuging and is deposited in the desorption column, in which it is subsequently washed with water acidified to a pH of less than 4 in order to remove the suspended solids retained.
When using packed columns, the acidified nejayote is filtered or centrifuged to remove suspended solids before being passed through the column. The operating temperature is from 20 to 50° C.; the velocity of the liquid varies between 3 and 8 volumes of packed bed per hour, with an end point fixed at a ferulic acid concentration in the effluent of not more than 5% of its initial concentration in the nejayote.
The adsorbed ferulic acid is recovered by desorption or elution with organic solvents such as ethanol or ethyl acetate. The elution temperature is between 50 and 70° C. The solvent is recycled through the column and its volume is equal to the free space of the packed column, which is between 25 and 40% of the bed depending upon the nature of the adsorbent material; the recycling time is between and 40 minutes, with 4 to 6 desorption cycles with fresh solvent.
The solvent is removed by evaporation, leaving a solid residue containing 65 to 95% of ferulic acid, depending upon the solvent used. The crude ferulic acid can be purified by recrystallization, gradually reducing the polarity of a concentrated solution in ethyl acetate by adding low polarity organic solvents such as methyl chloride and hexane, or by reducing the pH of an aqueous alkaline solution.
Patent document CN101845464 discloses a method for preparing ferulic acid from maize grains hydrolyzed by a multi-purpose enzyme. The method comprises steeping maize grains in NaOH in the dark, sterilizing at high pressure, adding a multi-purpose enzyme with peptidase and esterase activities to hydrolyze ester and peptide bonds in the cell wall, obtaining a supernatant by centrifuging, treating the supernatant in a chromatography column, eluting the concentrate obtained by extraction with ethyl acetate and obtaining ferulic acid through the use of a rotary evaporator.
Among the disadvantages encountered with the abovementioned processes there is the fact that the removal of suspended solids is partial and the remaining suspended solids cause the adsorbent material to become fouled and degraded, making it difficult to regenerate and reuse, increasing operating costs because this adsorbent material has to be disposed of.
Active carbon has a very short useful life, so large quantities of the material are required in order to implement a process using activated carbon on an industrial scale, and it has to be periodically replaced, thus increasing operating cost.
Another disadvantage is that carrying out desorption through recycling cycles is not the most suitable way because in the desorption process the material is transferred by a concentration gradient, and for this elution has to be performed continuously (input to output) without recycling, as this is the most efficient way of removing ferulic acid. Likewise the desorption suggested in the documents mentioned above is carried out at a temperature of 50 to 70° C., which involves an additional operating cost to raise and maintain the temperature of the solvent during the operation.
In these methods there is also no mention of separation of the impurities accompanying the ferulic acid, and these reduce the degree of purity of the final product. A greater number of purification steps are required in order to increase purity.
Another disadvantage of the prior art is that there is no handling and final disposal of the deferulized nejayote, the flows of water used for cleaning and regeneration of the adsorbent medium and the crystallization mother liquors; as a result of this all these effluents produced result in a loss of water.
Because of the abovementioned disadvantages, a method has been developed to obtain ferulic acid and/or its salts, and this is described below.